The mystery of who tried to keep thousands of Canadians from casting ballots in the last election will reach new heights Monday when voters go to court in hopes of getting the results in six ridings tossed out.

At the centre of the case are troubling questions about the widespread use of robocalls, or harassing live calls, to mislead voters about the location of their polling stations or discourage them from voting.

The controversy over voter suppression tactics has been building slowly since the election but took on added urgency last week when it was revealed Canada is conducting a criminal investigation of these tactics in 56 of the 308 federal ridings.

Beyond the validity of the 2011 results in the six contested ridings, the case that begins Monday in Federal Court in Ottawa has much wider implications for Canadian democracy.

“It calls into question the integrity of the whole election process,” University of Toronto political scientist Peter Russell said of the use of robocalls.

“Canadian citizens don’t want to be lied to in robocalls. If there’s no regulation of the use of technology and these technologies just keep coming on one after another, people are going to be pretty concerned that the electoral system isn’t secure.”

On Monday, lawyers for the eight voters who have raised the legal challenge will face off against lawyers for the six Conservative MPs who won the disputed ridings. The hearing is expected to last all week.

The case, which could end up before the Supreme Court of Canada, could break new ground in the laws governing elections.

“The court has never been confronted by a case like this and Canadians have never been confronted by evidence of widespread voter suppression having taken place in any election,” said Steven Shrybman, lawyer for the Council of Canadians, an advocacy group that is supporting the legal challenge.

But Fred DeLorey, spokesperson for the Conservative Party of Canada, said the legal challenge was politically motivated.

“It is increasingly apparent that this is a political activist campaign masquerading as a lawsuit — a left-wing group is seeking to overturn democratic elections because it doesn’t like how people voted,” DeLorey said in an email.

At stake are election results in the ridings of Nipissing-Timiskaming in Ontario; Elmwood-Transcona and Winnipeg South Centre in Manitoba; Saskatoon-Rosetown-Biggar in Saskatchewan; Vancouver Island North in B.C., and Yukon. The margins of victory were narrow in all six ridings, with the Conservative candidate winning by just 18 votes in Nipissing-Timiskaming.

A byelection would be called in any riding where the 2011 voting results were nullified by the courts.

Past cases of voting fraud or irregularities have involved questionable ballots or voting lists. But this case is about votes that might not have been cast at all as the applicants allege that harassing and misleading phone calls were made to “tens of thousands” of voters.

“The calls appear to have been part of a concerted and unprecedented effort to prevent the recipients from voting in the election,” says the filing on behalf of the eight voters.

But proving that position may not be easy.

“Unlike ballots in the box ... that shouldn’t be there, we’re having to prove a negative in a way, that there are ballots that weren’t cast ... that’s a significant challenge,” Shrybman said.

To make their case, the applicants are drawing on reports of misleading phone calls, purportedly from Elections Canada, that tried to steer voters to bogus polling stations. Other voters say they got harassing calls through the night from people claiming to be from rivals of the Conservatives in the ridings.

Their case also draws on a survey of 2,872 voters in the six ridings by pollster Frank Graves of EKOS Research Associates.

That survey found that Liberal, Green party and NDP supporters were more likely to receive the misleading calls than Conservative Party of Canada backers. It estimates that as many as 6,000 Canadians may have been deterred from voting in the six ridings.

“These activities were clearly targeted at (non-Conservative) voters in a manner that is highly improbable to have happened by chance,” their court documents say.

The applications suggest the Conservatives’ detailed voter database, known as Constituent Information Management System, is the “most likely source” of information used to make the “illicit calls.”

In its own court filing, the Conservative Party of Canada says the applicants have nothing more than “statistics and argument” to back their attempt to toss six sitting MPs from the House of Commons.

“Overturning an election is an extraordinary remedy of last resort,” it says.